can i flavor store bought wilton fondant and how much do i use?
You can, but if you are even the silghtest bit serious about selling a good product, don't. Wilton fondant is great for covering dummies and making embellishments that aren't meant to be eaten. And plus, it is the most expensive inedible medium you can buy!
Try some MMF or MFF-both recipes easily found in the recipe section on this very site.
Heck, if your serious about what you eat, you won't use Wilton's fondant. 
I use it in a pinch. But I will make some candy clay or mmf and do a 50/50 mix. I have used Lorann oils to flavor it, too. That is the only way it is edible to me. Otherwise, if you can get the Satin ice, do so!
I recommend that my students use half of a dram of LorAnn candy oil per 24 ounces (small box) of Wilton fondant, and then taste to see if they need to add more.
You can actually make it taste pretty good using candy oils! And if you use a 50% coupon at Michael's, you can pick up a 5 pound box for 10 bucks...making it quite inexpensive. 
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